1 files changed, 2 insertions, 2 deletions
diff --git a/lib/js/urweb.js b/lib/js/urweb.js
index d7bb7b6f..f05957a0 100644
--- a/lib/js/urweb.js
+++ b/lib/js/urweb.js
@@ -19,9 +19,9 @@ function plus(x, y) { return x + y; }
 function minus(x, y) { return x - y; }
 function times(x, y) { return x * y; }
 function div(x, y) { return x / y; }
-function divInt(x, y) { var n = x / y; return n < 0 ? Math.ceil(n) : Math.floor(n); }
+function divInt(x, y) { if (y == 0) er("Division by zero"); var n = x / y; return n < 0 ? Math.ceil(n) : Math.floor(n); }
 function mod(x, y) { return x % y; }
-function modInt(x, y) { var n = x % y; return n < 0 ? Math.ceil(n) : Math.floor(n); }
+function modInt(x, y) { if (y == 0) er("Division by zero"); var n = x % y; return n < 0 ? Math.ceil(n) : Math.floor(n); }
 function lt(x, y) { return x < y; }
 function le(x, y) { return x <= y; }